Rotary steerable technology belongs to the field of directional drilling, and is mainly used for drilling three trajectory wells such as directional wells, horizontal wells and extended reach wells, etc. Relying on a high-precision servo control mechanism and high-precision D&I measurement sensors, it can accurately control the drilling direction of a drill bit in real time, and thereby controls a wellbore trajectory. Existing conventional low-built-rate (6.5°/30 m) rotary steerable tools can't meet the requirements for drilling directional shale gas wells and offshore or land high-DLS wells anymore.
The AutoTrak Curve rotary steerable tool from Baker Hughes Incorporated employs three sets of hydraulic push-the-bit cylinders and their auxiliary ribs to push against the well wall. Under the pushing forces, the upper portion of the steerable tool is bent and deformed integrally, so that a fixed angle is formed between the axial direction of the wellbore trajectory and the axial direction of the steerable tool, and thereby a building angle is created. A disadvantage of such a structure is that bending the upper portion of the steerable tool consumes the pushing forces, and the bending caused by the pushing forces aggravates the bending stress in the drilling stem at the upper portion. Consequently, in a large-curvature wellbore, the drilling tool at the upper portion is prone to have alternating fatigue damages. As a result, there is a high requirement for the strength of the metal material of the drilling tool at the upper portion. It is hard for the steerable system to achieve a higher built rate, because the entire tool system is deformed integrally in the wellbore. Moreover, the ribs of the rotary steerable tool from Baker Hughes Incorporated suffer severe abrasion, since they push against the well wall.
The PD Archer rotary steerable tool from Schlumberger Limited employs a structure in which the main body of a measurement and control unit is articulated with the main body of a universal mechanism, four sets of pushing pistons located at the lower end of the main body of the measurement and control unit push against the inner wall of a steering sleeve around the main body of the universal mechanism at the lower portion, and thereby the direction of the drill bit is controlled. Since the tool system employs a full-rotary design concept and utilizes mud pressure to drive the pistons, the steering sleeve around the main body of the universal mechanism bears high force, may be worn out more easily in a rotation state, and has a short service life. Furthermore, the pistons are hard to seal and may have a shortened service life because the mud contains sand. Consequently, the entire rotary steerable tool system has a short overall service life and involves a higher maintenance and service cost.